Replaced by an updated figure. The labels of crRNA-DNMT-(+4) and crRNA-DNMT-23nt were placed in the wrong order, and the correct order should be "M, control, crRNA-DNMT-(-8), crRNA-DNMT-23nt, crRNA-DNMT-(+4) and crRNA-DNMT-(+8). The order of the crRNA names in the bottom illustrative figure was correct.